ar_measure_flutter

AR for Flutter with the two primitives you need to build a measuring experience — the Apple-Measure style "aim a reticle, tap to place" flow — on ARCore and ARKit.

Most Flutter AR plugins surface only a tap hit test, and give you no way to draw Flutter widgets that stay attached to the real world. This package adds:

Capability	Why it matters
Hit test at any screen point	Drives a crosshair/reticle that continuously reports what it is aimed at, without waiting for a tap.
Per-frame camera matrices	Lets you project world positions back to screen pixels, so Flutter-drawn lines and labels stay glued to the object as the camera moves.

Both arrive on one throttled native callback, so a live reticle costs a single message per sample rather than a method-channel round-trip every frame.

Fork notice. This is a fork of ar_flutter_plugin_2 by Hugo Lefèvre, itself a fork of the original ar_flutter_plugin. All of the original AR session, anchor, object and cloud-anchor functionality is retained and unmodified — this fork exists to add the two capabilities above. Licensed MIT, with the upstream copyright preserved in LICENSE.

Install

dependencies:
  ar_measure_flutter: ^0.1.0

The additions

Per-frame updates

Enable a throttled stream of AR state. x / y are the reticle position in device pixels — screen centre is the usual choice.

sessionManager.onFrameUpdate = (ARFrameUpdate? update) {
  final hit = update?.reticleHit;               // null when not on a surface
  final world = hit?.worldTransform.getTranslation();
};

final media = MediaQuery.of(context);
final size = media.size * media.devicePixelRatio;
await sessionManager.setFrameUpdates(
  true,
  x: size.width / 2,
  y: size.height / 2,
  hz: 20,
);

Stop the stream when leaving the screen:

await sessionManager.setFrameUpdates(false);

Projecting world → screen

ARFrameUpdate.project() converts a world position to a pixel coordinate inside viewport, or null when the point is behind the camera.

final projected = update.project(worldPosition);
if (projected != null) {
  // viewport is device pixels; Flutter lays out in logical pixels
  final dpr = MediaQuery.devicePixelRatioOf(context);
  final onScreen = Offset(projected.dx / dpr, projected.dy / dpr);
}

This is what keeps a CustomPainter overlay attached to the real world: store world positions only and re-project them every frame. Storing the pixel coordinate captured at placement time looks correct until the camera moves.

One-shot hit test

For a single probe without enabling the stream:

final hit = await sessionManager.hitTestAtScreenPosition(x, y);

Platform support

	Android	iOS
Screen-point hit test	✅ ARCore	⚠️ not yet wired
Camera matrices	✅ ARCore	⚠️ not yet wired
All original plugin features	✅	✅

The new APIs are implemented on Android (ARCore) today. The ARKit equivalents exist (ARSCNView.hitTest, camera.projectionMatrix) but are not yet bridged — contributions welcome. Everything inherited from upstream works unchanged on both platforms.

Requirements

• Android: an ARCore-capable device
• A physical device — AR does not run in emulators or the iOS Simulator

Credits

• Original plugin: ar_flutter_plugin
• Direct upstream: ar_flutter_plugin_2 by Hugo Lefèvre